1. Field of the Invention
The present invention relates to a method for producing optically active compounds such as optically active alcohols and optically active amines. More specifically, the present invention relates to a novel, highly practical method for producing optically active compounds useful for various utilities such as intermediates for synthesizing pharmaceutical chemicals, liquid crystal materials and agents for optical resolution.
2. Description of the Related Art
Various methods for producing optically active compounds have been known conventionally. As the method for asymmetrically synthesis of optically active alcohol compounds, for example, the following methods have been known;                (1) a method by using enzymes such as baker's yeast; and        (2) a method for asymmetric hydrogenation of carbonyl compounds by using metal complex catalysts. For the method (2), in particular, a great number of examples of asymmetric catalytic reactions have been reported for example as follows;        (1) an asymmetric hydrogenation of carbonyl compounds with functional groups, by means of optically active ruthenium catalysts, as described in detail in Asymmetric Catalysis in organic Synthesis, Ed. R. Noyori., pp. 56-82 (1994); (2) a method through hydrogen transfer-type reduction by means of chiral complex catalysts of ruthenium, rhodium or iridium, as described in Chem. Rev., Vol. 92, pp. 1051-1069 (1992); (3) a process of asymmetric hydrogenation tartaric acid by means of a modified nickel catalyst with tartaric acid as described in Oil Chemistry, pp.882-831 (1980) and Advances in Catalysis, Vol.32, pp.215 (1983), Ed. Y. Izumi; (4) an asymmetric hydrosilylation method, as described in Asymmetric Synthesis, Vol.5, Chap.4 (1985), Ed. J. D. Morrison and J. Organomet. Chem. Vol.346, pp.413-424 (1988); and (5) a borane reduction process in the presence of chiral ligands as described J. Chem. Soc., Perkin Trans.1, pp.2039-2044 (1985) and J. Am. Chem. Soc., Vol.109, pp. 5551-5553 (1987).        
By the conventional method by means of enzymes, however, alcohols can be recovered at a relatively high optical purity, but the reaction substrate therefor is limited and the absolute configuration in the resulting alcohols is limited to specific one. By the asymmetric hydrogen hydrogenation method by means of transition metal complex catalysts, optically active alcohols can be produced at a high selectivity, but a pressure-resistant reactor is required therefor because hydrogen gas is used as the hydrogen source, which is disadvantageous in terms of operational difficulty and safety. Furthermore, the method through such asymmetric hydrogen transfer-type reduction by using conventional metal complex catalysts is limited in that the method requires reaction conditions under heating and the reaction selectivity is insufficient, disadvantageously in practical sense.
Accordingly, it has been desired conventionally that a new, very general method for synthesizing optically active alcohols by using a highly active and highly selective catalyst with no use of hydrogen gas be achieved.
But no highly efficient and highly selective method for producing such secondary alcohols through asymmetric synthetic reaction by using catalysts similar to those described above has been established yet. As to the optically active secondary alcohols, a method for synthesizing optically active secondary alcohols via optional resolution of racemic secondary alcohols has been known for some reaction substrate which can hardly be reduced, although an excellent optical purity is hardly attained. (Asymmetric Catalysis in Organic Synthesis, Ed. R. Noyori). Because hydrogen transfer-type reduction is a reversible reaction according to the method, dehydrogenation-type oxidation as its adverse reaction is used according to the method. Therefore, the method is called as kinetic optical resolution method. According to the method, however, no process of producing optically active secondary alcohols with catalysts at a high efficiency has been reported yet.
As the method for synthetically producing optically active amine compounds, furthermore, a process of optically resolving once produced racemic compounds by using optically active acids and a process through asymmetric synthetic reaction have been known. By the optical resolution process, however, optically active acids should be used at an equal amount or more to amine compounds disadvantageously and complex procedures such as crystallization, separation and purification are required so as to recover optically active amine compounds. As the method through asymmetric synthesis, alternatively, the following processes have been known; (1) an enzymatic process; (2) a process by using metal hydride compounds; and (3) a process of asymmetric hydrogenation by using metal complex catalysts. As to the process by using metal hydride compounds as described above in (2), a great number of reports have been issued about a process of asymmetrically reducing carbon-nitrogen multiple bonds by using an metal hydrides with chiral modifiers. As a general process thereof, for example, it has been known a stoichiometric reduction process of imine compounds and oxime compounds by using a metal hydrides with an optically active ligand, as described in Comprehensive Organic Synthesis, EdS. B. M. Trost and I. Flemming, Vol.8, p.25 (1991), Organic Preparation and Procedures Inc. O. Zhu, R. O. Hutchins, and M. K. Huchins, Vol.26(2), pp.193-235 (1994) and Japanese Patent Laid-open No. 2-311446. The process includes a number of processes with excellent reaction selectivity, but these processes are disadvantageous because that these processes require the use of a reaction agent at an equivalent weight or more to a reaction substrate, along with neutralization treatment after the reaction and additionally in that these processes require laborious purification procedures to recover optically active substances. As the process of asymmetric hydrogenation of carbon-nitrogen multiple bonds by using metal complex catalysts as the method (3), it has been known an asymmetric hydrogenation process of imine compounds with functional groups, by means of optically active metal complex catalysts, as described in Asymmetric Catalysis inorganic Synthesis, pp.82-85 (1994), Ed. R. Noyori. But the process has a drawback in terms of reaction velocity and selectivity.
By the method by using enzymes as the method (1), furthermore, amines at a relatively high optical purity can be recovered, but the reaction substrates are limited and the resulting amines have only specific absolute configurations. Furthermore, at a process of asymmetric hydrogenation by means of complex catalysts of transition metals using hydrogen gas, optically active amines have not yet been recovered at a high selectivity or pressure-resistant reactors are essentially required because hydrogen gas is used as the hydrogen source. Hence, such process is disadvantageous because of technically difficult operation and safety problems.
Accordingly, it has been demanded that a novel method for synthesizing an optically active amine by using a very common, highly active and highly selective catalyst be realized.
Alternatively, a great number of transition metal complexes have been used conventionally as catalysts for organic metal reactions; particularly because rare metal complexes are highly active and stable with the resultant ready handleability despite of high cost, synthetic reactions using the complexes have been developed. The progress of such synthetic reactions using chiral complex catalysts is innovative, and a great number of reports have been issued, reporting that highly efficient organic synthetic reactions have been realized.
Among them, a great number of asymmetric reactions using chiral complexes catalysts with optically active phosphine ligands as the catalysts therefor have already been developed, and some of them have been applied industrially (Asymmetric Catalysis in Organic Synthesis, Ed. R. Noyori).
As complexes of optically active nitrogen compounds coordinated with transition metals such as ruthenium, rhodium and iridium, a great number of such complexes additionally having excellent properties as catalysts for asymmetric synthetic action have been known. So as to enhance the properties of these catalysts, a great number of propositions concerning the use of optically active nitrogen compounds of specific structures have been done (Chem. Rev., Vol.92, pp.1051-1069 (1992)).
For example, reports have been issued about (1) optically active 1,2-diphenylethylenediamines and rhodium-diamine complexes with ligands of cyclohexanediamines, as described in Tetrahedron Asymmetry, Vol.6, pp.705-718 (1995); (2) ruthenium-imide complex with ligands of optically active bisaryliminocyclohexanes, as described in Tetrahedron, Vol. 50, pp.4347-4354 (1994); (3) iridium-pyridine complex with ligands of pyridines, as described in Japanese Patent Laid-open Nos. 62-281861 and 63-119465; (4) optically active 1,2-diphenylethylenediamines or iridium-diamine complex with ligands of cyclohexanediamines, as described in Japanese Patent Laid-open No.62-273990; (5) ruthenium-diamine complex of RuCl[p-TsNCH(C6H5)CH(C6H5)NH2] (arene) (chloro-(N-p-toluenesulfonyl-1,2-diphenylethylenediamine)(arene)ruthenium) (arene represents benzene which may or may not have a substituent), which is produced by coordinating ruthenium with optically active N-p-toluenesulfonyl-1,2-diphenylethylenediamine [referred to as “p-TsNHCH(C6H5)CH(C6H5)NH2” hereinabove and below], as described in J. Am. Chem. Soc., Vol.117, pp.7562-7563(1995); J. Am. Chem. Soc., Vol.118, pp.2521-2522 (1996) and J. Am. Chem. Soc., Vol.118, pp.4916-4917 (1996).
Even if these complexes are used, however, problems currently remain to be overcome for practical use, including insufficient catalyst activities, sustainability and optical purities, depending on the subjective reactions and reaction substrates.